# 24 Lecture

## Examples of Thevenin's Theorem

Thevenin's theorem is a powerful tool in circuit theory that simplifies complex circuits into simpler circuits that are easier to analyze and understand. It allows us to replace a complex network of resistors, capacitors.

## Important Mcq's Midterm & Finalterm Prepration Past papers included

What is the equivalent resistance for the circuit shown below when looking from terminals A and B using Thevenin's theorem?

5?      10?

A ----/\/\/\----/\/\/\---- B

a. 3.33?

b. 7.5?

c. 15?

d. 50?

Answer: b. 7.5?. The equivalent resistance is the sum of the two resistors: 5? + 10? = 15?. Then, the Thevenin resistance is the same as the equivalent resistance: 7.5?.

What is the Thevenin voltage for the circuit shown below when looking from terminals A and B using Thevenin's theorem?

20V

A ---/\/\/\---/\/\/\--- B

10?    5?

a. 10V

b. 15V

c. 20V

d. 25V

Answer: c. 20V. To find the Thevenin voltage, we need to calculate the voltage across the terminals A and B when the circuit is open. This is the same as the voltage across the 5? resistor, which is given as 20V.

What is the equivalent circuit for the circuit shown below when looking from terminals A and B using Thevenin's theorem?

5?      10?

A ----/\/\/\----/\/\/\---- B

a. 7.5V voltage source in series with a 7.5? resistor

b. 10V voltage source in series with a 15? resistor

c. 20V voltage source in series with a 10? resistor

d. 15V voltage source in series with a 5? resistor

Answer: a. 7.5V voltage source in series with a 7.5? resistor. We found in question 1 that the equivalent resistance is 7.5?, and in question 2 that the Thevenin voltage is 20V. Therefore, the equivalent circuit is a 7.5V voltage source in series with a 7.5? resistor.

What is the Thevenin voltage for the circuit shown below when looking from terminals A and B using Thevenin's theorem?

6V          4V

A ---/\/\/\---/\/\/\---/\/\/\--- B

2?          4?     2?

a. 4V

b. 6V

c. 8V

d. 10V

Answer: b. 6V. To find the Thevenin voltage, we need to calculate the voltage across the terminals A and B when the circuit is open. This is the same as the voltage across the 4? and 2? resistors in series, which is given as 6V.

What is the Thevenin resistance for the circuit shown below when looking from terminals A and B using Thevenin's theorem?

3?

A ---/\/\/\----/\/\/\--- B

6?        9?

a. 6?

b. 8?

c. 9?

d. 12?

Answer: a. 6?. The equivalent resistance is the sum of the two resistors in parallel

## Subjective Short Notes Midterm & Finalterm Prepration Past papers included

What is Thevenin's theorem?

Answer: Thevenin's theorem is a theorem in circuit theory that states that any linear network of resistors, capacitors, and other components can be replaced with an equivalent circuit consisting of a single voltage source and a series resistance.

What is the purpose of Thevenin's theorem?

Answer: The purpose of Thevenin's theorem is to simplify complex circuits into simpler circuits that are easier to analyze and understand.

How do you apply Thevenin's theorem to a circuit?

Answer: To apply Thevenin's theorem, you first select two points in the circuit and remove all the components to the right of these points. You then calculate the Thevenin voltage and resistance using the components to the left of the selected points.

What is the Thevenin voltage?

Answer: The Thevenin voltage is the open-circuit voltage at the selected points in the circuit after all the components to the right of these points have been removed.

What is the Thevenin resistance?

Answer: The Thevenin resistance is the equivalent resistance of the circuit at the selected points after all the components to the right of these points have been removed.

What is the purpose of selecting two points in the circuit for Thevenin's theorem?

Answer: The purpose of selecting two points in the circuit is to determine the Thevenin voltage and resistance of the circuit at these points.

Can Thevenin's theorem be applied to AC circuits?

Answer: Yes, Thevenin's theorem can be applied to AC circuits by calculating the impedance of the circuit instead of the resistance.

What is the purpose of using Thevenin's theorem to simplify a circuit?

Answer: The purpose of using Thevenin's theorem to simplify a circuit is to make it easier to analyze and understand, and to reduce the number of components in the circuit.

What is the advantage of using Thevenin's theorem in circuit analysis?

Answer: The advantage of using Thevenin's theorem in circuit analysis is that it simplifies complex circuits into simpler circuits that are easier to analyze and understand, which can save time and reduce errors in circuit design.

Can Thevenin's theorem be applied to non-linear circuits?

Answer: No, Thevenin's theorem can only be applied to linear circuits that obey the principle of superposition.

### Examples of Thevenin's Theorem

Thevenin's theorem is a powerful tool in circuit theory that simplifies complex circuits into simpler circuits that are easier to analyze and understand. It allows us to replace a complex network of resistors, capacitors, and other components with a simpler equivalent circuit consisting of a single voltage source and a series resistance. In this article, we will discuss several examples of Thevenin's theorem and how it can be applied to real-world circuits. Example 1: DC Voltage Divider Consider the circuit shown below, which is a simple DC voltage divider consisting of two resistors connected in series. The circuit is powered by a DC voltage source V1. lua Copy code +---R1----+ | | V1 --+---R2----+-- 0V | | +----------+ To apply Thevenin's theorem, we first select two points in the circuit, such as the points A and B shown below. css Copy code +---R1----+ | | V1 --+---R2----+-- 0V | | +----A-----+----B----+ We then remove all the components to the right of these points, leaving only the components to the left. In this case, the only component to the left is R1. We measure the voltage at the points A and B and find that the voltage at point A is equal to V1 times the resistance of R2 divided by the sum of the resistances of R1 and R2. We can calculate the Thevenin resistance by shorting the voltage source and calculating the equivalent resistance of the circuit. In this case, the Thevenin resistance is equal to the sum of R1 and R2. Example 2: AC Circuit Thevenin's theorem can also be applied to AC circuits. Consider the AC circuit shown below, which consists of a voltage source V1, a resistor R1, and a capacitor C1. lua Copy code +---R1----+ | | | V1 --+----+-----+-- 0V | | | +---C1----+ To apply Thevenin's theorem, we again select two points in the circuit, such as the points A and B shown below. css Copy code +---R1----+ | | | V1 --+----+-----+-- 0V | | | +---C1----+----A----+----B----+ We then remove all the components to the right of these points, leaving only the components to the left. In this case, the only component to the left is R1. We can calculate the Thevenin voltage by calculating the voltage across R1 using Ohm's law. The voltage across R1 is equal to the product of the current through R1 and the resistance of R1. The current through R1 is equal to the voltage source divided by the impedance of the circuit, which is equal to the square root of the sum of the squares of the resistance and the reactance. The Thevenin resistance is equal to the resistance of R1. Example 3: Transistor Amplifier Thevenin's theorem can also be used to simplify more complex circuits, such as transistor amplifiers. Consider the circuit shown below, which is a simple common-emitter amplifier. css Copy code +--R1--+ | | Vin -+--R2--+--B | | +--C1--+--Vout | | +------+- 0V To apply Thevenin